3. Answer all parts (a) to (t) of this question. Consider a function 2 2 7r(:n,y) = 10 a:2 y2+a$y+be'\" +9, where a: E R, y E R and (a, b) are parameters. (e) [5 marks] Show that if b > 0, then (x = 0; y = 0) is not a global maximum